Most direct conversion radio frequency receivers require baseband correction for a mismatch between the in-phase (I) and quadrature (Q) paths, which is referred to as I/Q mismatch. The receiver downconverts a quadrature baseband signal from a radio frequency signal to a quadrature baseband signal. More specifically, the receiver includes a first mixer that mixes the radio frequency signal with an in-phase component of a local oscillator signal to downconvert the radio frequency signal to an in-phase component of the quadrature baseband signal. Similarly, the receiver includes a second mixer that mixes the radio frequency signal with a quadrature component of the local oscillator signal to downconvert the radio frequency signal to a quadrature component of the quadrature baseband signal.
However, the gain of the first mixer may not be matched to the gain of the second mixer. As a result, a gain error is introduced into the quadrature baseband signal. In addition, the in-phase component and the quadrature component of the local oscillator signal used by the mixers for downconversion may not be ninety degrees out-of-phase. As a result, a phase error, or quadrature error, is introduced into the quadrature baseband signal. Combined, the gain and quadrature errors form an I/Q mismatch of the receiver It is desirable to correct the I/Q mismatch of the receiver at baseband in order to provide improved performance.
Generally, baseband correction of the I/Q mismatch of the receiver is performed based on a 2×2 distortion matrix defining a relationship between the actual I and Q components having been distorted by the I/Q mismatch of receiver and the ideal I and Q components. However, the distortion matrix is not easily measured (i.e calibrated).
Thus, there remains a need for a system and method for providing baseband correction of an I/Q mismatch of a direct conversion radio frequency receiver and more particularly for calibrating the distortion matrix used to compensate for the I/Q mismatch of the receiver.